1. Technical Field
The present invention relates to a technique for reducing display defects in a liquid crystal panel.
2. Related Art
Liquid crystal panels each include: a pair of substrates, in one of which pixel electrodes are arranged in matrix so as to correspond to respective pixels, and in the other of which a common electrode is disposed in common for the pixels; and liquid crystal interposed between the pixel electrode and the common electrode. In such a configuration, when a voltage according to a gray-scale level is applied and held between the pixel electrode and the common electrode, the alignment state of the liquid crystal is defined for each pixel, whereby the transmittance or reflectance is controlled. Accordingly, it can be said in the configuration that, among electric fields acting on liquid crystal molecules, only a component in a direction from the pixel electrode toward the common electrode (or the opposite direction), that is, a component in a direction perpendicular to the substrate surface (vertical direction) contributes to display control.
As a pixel pitch is narrowed for miniaturization and higher resolution as in recent years, an electric field generated between pixel electrodes next to each other, that is, an electric field in a direction parallel to the substrate surface (lateral direction) is generated, and the influence thereof is becoming non-negligible. For example, when a lateral electric field is applied to liquid crystal that should be driven by a vertical electric field as in the vertical alignment (VA) mode or the twisted nematic (TN) mode, an alignment defect of liquid crystal (reverse tilt domain) occurs, causing a display defect.
For reducing the influence of the reverse tilt domain, a technique for devising the structure of a liquid crystal panel by, for example, defining a light shielding layer (an opening) according to the shape of a pixel electrode (refer to JP-A-6-34965 (FIG. 1), for example) has been proposed. Moreover, for example, a technique for clipping a video signal having a set value or more based on the determination that a reverse tilt domain is generated when an average luminance value calculated from a video signal is equal to or less than a threshold value (refer to JP-A-2009-69608 (FIG. 2), for example) has been proposed.
However, the technique for reducing the reverse tilt domains with the structure of the liquid crystal panel has such drawbacks that the aperture ratio is likely to decrease, and that the technique cannot be applied to an existent liquid crystal panel that has been manufactured without devising its structure. On the other hand, the technique for clipping a video signal having a set value or more has such a drawback that the brightness of an image to be displayed is uniformly limited to the set value.